1. Technical Field
The present invention relates to determining characteristics of liquids at sub-ambient temperatures and, more particularly, determining the pumpability limit, freeze point, and pour point at sub-ambient temperatures.
2. Background
As commercial aircraft fly over the North Pole for the shortest routes to Europe, fuel inside of the aircraft are subject to very low temperatures. In making such flights, it is important to know the suitability of the fuel before it is loaded onto the aircraft. The flight plans of the aircraft may be altered to fly at lower altitudes, or a different route may be taken, if the fuel is not suitable for such very low temperatures as may be encountered. If it is suspected that the aircraft fuel would freeze or form solid crystals, either of which would not be amenable to optimized flow, the crew could alter the flight path so the aircraft does not experience such low temperatures. The alternate flight path could be as simple as flying at lower altitudes where the temperature is warmer.
In the past, the jet fuel was characterized by its freeze point. An aircraft would not fly in such a condition that the freeze point of the fuel is ever reached.
A few years ago, the International Air Transport Association (IATA) asked the Coordinating Research Counsel (CRC) to take a look at freeze point and determine if it was the best way to characterize the jet fuel. As a result of such research, it was determined that freeze point was probably not the best way to characterize the jet fuel at sub-ambient temperatures. The conclusion was reached that viscosity was probably a better way to characterize the jet fuel at sub-ambient temperatures.
Cambridge Viscosity, Inc., the assignee of the present patent application, manufactures and sells a viscometer as shown in U.S. Pat. No. 7,614,285, issued on Nov. 10, 2012, entitled “Dynamic Reciprocating—Bob Rheometry.” The viscometer is used to measure the viscosity of all type of fluids. Viscosity of a fluid is determined by the time for a bob or piston to reciprocate in the fluid under constant magnetic force. There has not been a suggestion to use the viscometer at sub-ambient temperatures.